1. Field of the Invention
The present invention relates to an external additive for an electrophotographic toner, a method for manufacturing the external additive, an electrophotographic toner using the external additive, and an image forming apparatus using the toner. More particularly, the present invention relates to an external additive for an electrophotographic toner useful for monochrome or full color image forming apparatus using electrophotography, such as copiers, laser printers and facsimile machines.
2. Discussion of the Background
Image forming processes such as electrophotography, electrostatic recording and electrostatic printing typically include the following processes.
(1) an imagewise electrostatic latent image is formed on an image bearing member such as photoreceptors and dielectric materials (electrostatic latent image forming process);
(2) the electrostatic latent image is developed by a developer including a toner to form a toner image on the image bearing member (developing process);
(3) the toner image is then transferred onto a receiving material such as paper optionally via an intermediate transfer medium (transfer process); and
(4) the toner image on the receiving material is fixed thereon, for example, upon application of heat and pressure.
As the developer, two-component developers including a carrier and a toner, and one-component developers including a magnetic or non-magnetic toner and not including a carrier, are known.
The toners are classified into positively-charge toners and negatively-charged toners. As the materials which impart a positive charge to a toner, charge controlling agents such as nigrosine dyes and quaternary ammonium salts, coating agents such as acrylic resins, fluorine-containing resins and silicone resins which are coated on the surface of a carrier, etc., are known.
As the materials which impart a negative charged to a toner, charge controlling agents such as metal-containing azo dyes, additives such as inorganic fillers and organic fillers, coating agents which are coated on the surface of a carrier, are known.
In addition, it is proposed that in order to improve the fluidity and charging properties of a toner, an inorganic filler such as metal oxides is mixed with toner particles. Such an inorganic filler is called as an external additive.
Further, it is also proposed that the surface of such an inorganic filler is treated with an agent such as silane coupling agents, titanate coupling agents, silicone oils and organic acids or coated with a resin, to improve the hydrophobic property and charging properties of the inorganic filler.
Specific examples of such inorganic fillers include silica, titanium oxide (titania), aluminum oxide, zinc oxide, magnesium oxide, cerium oxide, iron oxide, copper oxide and tin oxide. In particular, hydrophobized particulate silicas which are prepared by reacting silica with an organic silicon compound such as dimethyldichlorosilane, hexamethyldisilazane and silicone oils to substitute the silanol groups on the surface of the silica with an organic group are preferably used. Among these hydrophobizing agents, silicone oils are preferable because the treated inorganic fillers have good hydrophobic property, and the resultant toner has low surface energy and thereby the toner has good transferability.
Japanese Patent Publication No. 07-3600 and Japanese Patent No. 2,568,244 have disclosed that a silica treated with a silicone oil and having a specific hydrophobic degree is used as an external additive.
In addition, in Japanese Laid-Open Patent Publications Nos. 07-271087 and 08-292598, addition quantity of a silicone oil serving as a treating agent and the content of carbon in the external additive are specified.
By these methods, the requirements such that an inorganic filler serving as a mother material of the external additive has to be hydrophobized and the charge properties of the resultant developer have to be stabilized even under high humidity conditions can be fulfilled.
However, a positive action to decrease adhesion of the resultant toner to various members in image forming apparatus, such as contact chargers, developer bearing members (i.e., sleeves), doctor blades, carriers, electrostatic latent image bearing members (i.e., photoreceptors) and intermediate transfer media, has not been taken.
In particular, when adhesion of a developer to a photoreceptor is too strong, problems tend to occur such that the resultant toner image has background fouling and/or the resultant character images, line images and dot images have omissions at their edge portions or center portions. These problems cannot be solved only by adjusting the addition quantity of the silicone oil to be added and/or the hydrophobic degree of the resultant external additive.
In addition, an image omission problem such that the resultant toner cannot be transferred onto recessed portions of a rough receiving material cannot be solved by these methods.
Japanese Laid-Open Patent Publication No. 11-212299 discloses an inorganic filler which includes a liquid silicone oil in a specific amount. However, as mentioned above, the above-mentioned problems cannot be solved by such a method (i.e., a method of adjusting the addition quantity of a hydrophobizing agent). In addition, there are no answers in the patent publication to the following questions:
(1) xe2x80x9cHow should an inorganic filler be treated with a silicone oil in order to effectively solve the problems?xe2x80x9d; and
(2) xe2x80x9cWhat is the structure of the effective silicones oil or their equivalents?xe2x80x9d
In addition, the patent publication (JOP 11-212299) does not mention about the preferable functional component and structure of the treating agent and the preferable mixing state of such a treating agent with an inorganic filler.
Because of these reasons, a need exists for an external additive by which a toner which does not contaminate various image forming members such as chargers, developing devices, photoreceptors, and intermediate transfer media and can produce high quality toner images without causing background fouling and image omissions even when the toner is used for a long period of time can be produced.
Accordingly, an object of the present invention is to provide an external additive by which a toner which does not contaminate various image forming members such as chargers, developing devices, photoreceptors, and intermediate transfer media and can produce high quality toner images without causing background fouling and image omissions even when the toner is used for a long period of time can be produced.
Another object of the present invention is to provide a method for effectively manufacturing such an external additive.
Yet another object of the present invention is to provide a toner which does not contaminating various image forming members such as chargers, developing devices, photoreceptors, and intermediate transfer media and can produce high quality toner images on various receiving materials without causing background fouling and image omissions even when used for a long period of time.
A further object of the present invention is to provide a developing device which can produce high quality toner images on various receiving materials without causing background fouling, image omissions and scattered images even when the toner is used for a long period of time.
Briefly these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by an external additive for a toner, which has an average particle diameter not greater than 100 nm and which includes an inorganic particulate material and a hydrophobizing agent, which agent is present on the surface of the inorganic particulate material in an amount of Ws by weight and present as a free hydrophobizing agent in an amount of Wf by weight, wherein a residual ratio {Ws/(Ws+Wf))xc3x97100 is from 40 to 98.5%, and wherein when at least one of a compound having an organopolysiloxane structure and a compound having a ring siloxane structure is detected when the external additive is analyzed by a pyrolysis gas chromatography mass spectroscopy (Py-GCMS) method after the external additive is washed by chloroform.
The compound having an organopolysiloxane structure preferably has the following formula (1): 
wherein R represents an alkyl group having from 1 to 3 carbon atoms; Rxe2x80x2 represents a silicone oil modification group such as an alkyl group, a halogenated alkyl group, a phenyl group or a modified phenyl group; Rxe2x80x3 represents an alkyl group having from 1 to 3 carbon atoms or an alkoxyl group; and n and m are independently an integer and satisfy the following relationship:
1xc2x7(n+m) 
The compound having a cyclic siloxane structure preferably has the following formula (2): 
wherein R represents an alkyl group having from 1 to 3 carbon atoms; Rxe2x80x2 represents a silicone oil modification group such as alkyl group, a halogenated alkyl group, a phenyl group or a modified phenyl group; and n is an integer not less than 3, and preferably not less than 4.
The hydrophobizing agent is preferably a silicone oil or a silicone varnish, and the inorganic particulate material is preferably silica, titanium oxide or alumina.
In another aspect of the present invention, a method for manufacturing an external additive for a toner is provided which includes the step of treating an inorganic particulate material with a hydrophobizing agent while heating such that the resultant external additive mentioned above is prepared. Alternatively the heating operation may be performed after the hydrophobizing treatment.
In yet another aspect of the present invention, a toner is provided which includes a colorant, a binder resin and the external additive mentioned above, wherein the toner has a volume average particle diameter not greater than 15 xcexcm and an agglomeration degree of from 5 to 70%. The toner may include a second external additive having an average primary particle diameter smaller than that of the first-mentioned external additive, and/or a particulate resin serving as a third external additive and having an average particle diameter greater than the average primary particle diameter of the first-mentioned external additive.
In a further aspect of the present invention, an image forming apparatus is provided which includes an image bearing member configured to bear an electrostatic latent image thereon, an image developer configured to develop the latent image with a developer including the toner mentioned above to form a toner image on the image bearing member, an image transferer configured to transfer the toner image onto a receiving material optionally via an intermediate transfer medium while contacting the image bearing member with the receiving material (or the intermediate transfer medium) therebetween.
The latent image may be plural electrostatic latent images formed on respective areas of the image bearing member or plural image bearing members. Each of the plural latent images is developed with a different color developer including a color toner to form plural color toner images onto a receiving material one by one or at the same time, wherein the color toner is the toner of the present invention.
The image developer may include plural color image developing sections each including a developing roller configured to bear a different color developer and a regulating blade configured to form a developer layer on the developing roller, wherein the color developer is the toner of the present invention.
The image forming apparatus may have plural image bearing members on which a different color toner image is formed. The plural color toner images are transferred on a receiving material one by one or transferred on an intermediate transfer medium one by one and then transferred onto a receiving material at the same time.
As the developer for use in the image forming apparatus, both one-component developers and two-component developers can be used.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.